1. Field of the Invention
The present invention relates generally to the field of liquid crystal display devices, and, more particularly, to a novel liquid crystal display structure having optimized on-off contrast ratio for implementation as part of a liquid crystal display panel.
2. Discussion of the Prior Art
Normally, a liquid crystal cell gap thickness is determined and built, and the applied voltage placed across the liquid crystal will determine the amount of optical transmission. Since the on-off contrast ratio is the maximum to minimum light transmission ratio, a small voltage shift in the liquid crystal optical transmission versus voltage characteristics, for example, can change the minimum transmission enormously and degrade the on-off contrast ratio. In addition, the future trend in scaling to ever higher bit (more gray levels) displays produces a more stringent requirement on the hysteresis of the transmission versus voltage characteristics. One such change in the transmission versus voltage characteristics can occur as a result of a change in operating temperature. A second such change in the transmission versus voltage characteristics will result if a light valve designed with a liquid crystal cell gap for one wavelength of light (or color) is used with another wavelength of light.
There exists liquid crystal display devices that employ temperature sensing to control the optical transmission properties of screen displays. U.S. Pat. No. 5,717,421 describes a system for correcting display panel drive signals based on a detected current signal associated with a pixel. In the system described, parameters are measured to determine current threshold characteristics of a pixel and the display is accordingly corrected based on detected threshold data and sensed temperature data of the display panel.
U.S. Pat. No. 5,694,147 describes a system for controlling the temperature of the liquid crystal material utilizing a temperature sensor and a servo external to the liquid crystal display. In the system described, temperature sensing circuitry implements a resistive Wheatstone bridge for incorporation in proximity to a liquid crystal display panel. A control circuit is provided to control the liquid crystal display temperature, and implements a bipolar transistor and a resistive heating element. Because of this system's external and non-integrated approach for maintaining temperature control, this technique is relatively inefficient and expensive to implement.
Thus, it would be highly desirable to provide a on-off contrast ratio optimization technique employing a temperature compensation and control system for a liquid crystal display device that is efficient, cost-effective, and integrated as part of high-contrast liquid crystal panel displays.